The present invention relates to natural materials which can be used as adhesives and binders. Natural carbohydrate and protein materials are used as binders and adhesives in a variety of applications. Carbohydrate materials, and in particular starches, are well known for use as components of adhesive compositions such as corrugating adhesives for paper and paperboard. A particularly useful corrugating adhesive comprises starch which is cooked in the presence of borax and caustic.
Starches are also used as binders in the paper industry in applications such as binders for light weight coatings. Cationic starches are also known to be useful as wet-end adhesives in paper manufacture. In addition, starch is known for use as a component in composite compositions such as those of Anderson et al., U.S. Pat. No. 5,385,764 and Anderson et al., U.S. Pat. No. 5,545,450 which comprise combinations of starch, fiber and calcium carbonate or other minerals.
Gums including alginates, gellan, locust bean and xanthan gum are known to provide particularly useful adhesive and binding properties at low concentrations when used in a variety of applications. Gums are particularly useful as binders in food compositions and particularly in composite food compositions.
Proteins provide excellent performance as adhesives and as binders in a number of applications but are reserved for use in certain specialized applications because they are generally more expensive than starches. Typical protein adhesives and glues include animal glues produced from collagen found in animal skin, connective tissue and bone. Fish glues made from the skin of fish such as cod also comprise collagen but with a lower molecular weight than other animal collagen. Casein protein is particularly useful in glues and in coatings for paperboard, plywood, door and furniture assembly because of the high adhesive strength which it provides. Glues produced from soy protein are useful as interior plywood glues, laminating glue for wood, door assembly, furniture assembly and other wood bonding applications. Blood proteins derived as byproducts of the meat industry also provide excellent adhesive properties and are used as adhesives in the manufacture of plywood and as bonding materials in sea foods such as surimi.
Potato plant tubers referred to herein as potatoes comprise several structures. Of these structures, the following make up the core from the center of the potato out: the pith, the vascular storage area, the vascular ring, followed by the so-called peel portion which consists of a cortex and a periderm. Approximate analysis of the entire white potato indicates about 77% water and solids of about 23%. Of the solids percentage, roughly 15% is starch and 2% is protein. The protein is located between the cortex and the periderm peel layer. In the processing of potatoes for food or industrial uses it is frequently desired to separate the potato peel from the heart of the potato, in order to make use of the substantially pure starch. The starch may be partially or completely gelatinized such that the peel is only weakly bound to the heart of the potato. Potato peel waste is thus produced as a byproduct in the processing of potatoes for food uses such as the manufacture of french fries, potato chips and in the processing of potatoes for industrial uses.
According to one method of processing potatoes to remove the potato skin, steam is directed against the exterior of potatoes such that the layer of starch immediately adjacent the potato peel is partially or completely gelatinized. The potato is then subjected to mechanical processing such that the peel with a layer of partially or completely gelatinized starch is separated from the heart of the potato which is then subjected to further processing. The resulting potato peel product comprises mostly water with the balance made up of gelatinized and ungelatinized starch, protein, fiber and ash. Prior to its disposal or other use the potato peel product is frequently combined with other waste streams containing byproducts of potato processing. Such streams of what is sometimes known as potato xe2x80x9ctrim wastexe2x80x9d contain potato trimmings and other byproducts of potato production. As such, the trim waste typically comprises relatively higher levels of starch (and where fryer waste from french fry production is combined, fat) and relatively lower levels of protein and fiber than does peel waste.
Whether or not the potato peel product includes potato trim waste, the potato peel waste product has little commercial value because it comprises a heterologous mixture of water, protein, fiber and starch. As a result potato peel products are usually disposed of as waste or are used as a liquid supplement to animal feed. Because the potato peel product can be costly to dispose of as waste and is expensive to transport and provides only marginal economic value when used as animal feed, there remains a desire in the art for new applications for potato peel products.
The present invention is based on the discovery that potato peel products such as derived from potato peel waste or potato peel waste in combination with potato trim waste are characterized by particularly useful properties as adhesives and binders in a variety of industrial and food product uses. Other uses for the potato peel products of the invention include use in oil well drilling mud, soy based adhesive coatings used in coated fine paper and in wet-end papermaking applications to increase bonding in brown paperboard. Potato peel products useful according to the invention can be derived in any of a variety of manners but are preferably potato peel waste such as produced by steam peeling potatoes. Alternatively, potato peel products useful according to the invention can be potato peel waste combined with potato trim waste and other materials.
While starches and certain proteins are known to be useful as adhesives and binders in various applications it has been found that the specific combination of gelatinized starch, ungelatinized starch, protein and fiber making up potato peel waste is characterized by particularly useful adhesive and binding properties. This is particularly the case when the potato peel products comprise potato starch which has not been completely gelatinized and those products are heated under conditions selected to complete gelatinization of the starch during setting of the adhesive or binder material.
Among other uses, the potato peel products of the invention may be used as adhesives and as binders in edible and non-edible composite materials. According to one aspect of the invention a non-edible composite material is provided which comprises a non-edible substrate and a binder wherein said binder comprises a potato peel product characterized on a dry solids basis by at least 30% starch, at least 5% protein and at least 2% fiber. Preferred potato peel products according to the invention comprise greater than 40%, more preferably greater than 50% and most preferably 55% to 65% starch on a dry solids basis; and from 2% to 20% fiber with 4% to 20% being preferred. Protein is preferably present at dry solids levels of from 5% to 30% with concentrations of 10% to 25% being particularly preferred.
Non-edible composite materials of the invention can comprise non-edible substrate materials including but not limited to mineral particles such as calcium carbonate, wood particles and fiber and paper fiber. Representative composite materials using potato peel products as binders according to the invention include materials such as gypsum wall board, acoustical tile, particle board and packaging materials.
The invention also provides a method of producing a non-edible composite material comprising a substrate and a binder wherein said binder comprises a potato peel product characterized on a dry solids basis by at least 30% starch wherein said starch is not completely gelatinized, at least 5% protein and at least 2% fiber to form a mixture; and heating said mixture under conditions selected to complete gelatinization of said starch.
Also provided by the invention are adhesive compositions comprising a potato peel product. One particularly preferred adhesive is that comprising a potato peel product characterized on a dry solids basis by at least 30% starch, at least 5% protein and at least 2% fiber which has been treated with borax and caustic.
The adhesive compositions of the invention are particularly useful for adhering paper or paperboard as corrugating and paper adhesives and also as labeling adhesives. According to one aspect of the invention the use of the potato peel products of the invention provide improvements in the printability of coated paper box and board containers. As corrugating adhesives the compositions of the invention provide particularly good properties for adhesion of both coated (including lightweight coated) and uncoated papers. The adhesives of the invention are also useful as architectural adhesives for use as wallpaper, tiling and paneling adhesives and are also particularly useful as adhesives in the production of architectural laminates including but not limited to plywood.
The potato peel products of the invention are also useful as binders in composite food products comprising an edible substrate and a binder. Suitable composite food products which can be produced according to the invention include meat analogs such as vegetable burger patties which can comprise soy protein as the substrate. Other composite food products which can comprise the potato peel products of the invention as binders include vegetable analogs and composite meat products including such products as sausage and surimi. Another food application is the binding of fat and water together in meat based sauces such as those used in Mexican and Italian cuisine.
The potato peel products of the invention can also be used in agriculture as soil binders to prevent silt migration in irrigated farming. Such binders would be superior to polyacrylamide flocculants currently used in such applications because of environmental concerns regarding the use of synthetic polymers. As such, the potato peel products of the invention may be added at concentrations of from 5 to 1000 ppm to irrigation water to prevent silt migration.
The potato peel products of the invention can also be used as binders in industrial applications such as in paper manufacture by being derivatized with a cationic substituent and used as a wet-end binder in paper manufacture. For this, suitable cationic derivatives include quaternary ammonium compounds can be used to derivatize the potato peel product according to methods known to the art.
Preferred levels of substitution with cationic reagents range from about 0.2 to about 2.0 cationic groups per anhydroglucose unit depending upon the intended application for the derivatized potato peel product with actual cationic substitution levels being less than those applied.
The potato peel products of the invention may also be derivatized with anionic substituents such as by oxidation with 0.9% chlorine based on a dry starch weight. Moreover, amphoteric potato peel products can be produced by a combination of cationic and anionic substitution. According to a further embodiment of the invention, charged coatings can be applied electrostatically by a dry coater apparatus.
Other preferred potato peel materials of the invention include potato peel waste which has been subjected to an oxidation reaction and is useful for increased adhesiveness. It is further contemplated that potato peel waste that has been subjected to a cross linking reaction with cross linking agents such as phosphorus oxychloride will exhibit useful properties as adhesives and wet end strength additives in the manufacture of paper.
In addition a potato peel product which has been treated with caustic demonstrates particularly good stability properties when stored for prolonged periods. Caustic addition can vary between 0.7% and 4% of peel waste with a pH measurement higher than 11 being preferred.
Other potato peel products which are useful according to the invention are those which are chemically modified by any of a variety of procedures which modify and improve the binding and adhesive properties of the product. Suitable chemical modifications include chemical derivatization including but not limited to oxidation, chemical crosslinking, anionic substitution, cationic substitution, modification by hydroxy-alkyl substitution and the like. While such chemical derivatization is expected to have its most significant effects on the starch content of the potato peel product it is also expected to have effects on the protein and fiber components of the potato peel products. Other chemical modifications of the potato peel product of the invention include hydrolytic modification of the potato peel product by acid or enzyme hydrolysis of the starch and other carbohydrate content of the product. It is further contemplated that the products can be subjected to enzymatic hydrolysis of the protein content by treatment with proteases.
Other potato peel products of the invention include those which are subjected to physical grinding to produce a particulate matter characterized by a particle size wherein 100% passes through a U.S. Standard No. 60 sieve.